Science Scoops: And…Reflections of Earth's Climate

by Stephen James O'Meara

Wondering how Earth's climate may be changing over the years? Well, how about keeping an eye on the Moon? Yup. That's what researchers did in the late 1920s, and that's what Philip R. Goode (New Jersey Institute of Technology) and his colleagues did more recently. Actually, Goode and his team are not directly watching the Moon. Instead, they're watching sunlight that has been reflected off the Earth and onto the Moon's “bright” side when it just happens to be in shadow, a phenomenon called “earthshine.” You see earthshine best when the Moon is in a crescent phase; it's the “old Moon in the new Moon's arms.” In essence, the scientists are using the Moon as a mirror, one that will reflect changes in Earth's atmosphere.

Here's how it works. The amount of sunlight our planet bounces back into space reflects how much cloud, atmospheric dust, and snow is covering the Earth. Any radiation not being reflected is being absorbed. This means that if the Earth isn't being as reflective as normal, Earth's climate must be getting warmer.

As reported in Sky & Telescope magazine, Goode says that on average the Earth reflects 30 percent of the sunlight hitting it. But recently our planet seems to be a bit brighter than it was in 1994–95. What does this mean?

Is the Earth getting colder?

Well, stay tuned, because the earthshine measurements will have to continue for many more years before the researchers can draw any conclusions.

Vocabulary

phenomenon:

An event or fact that can be felt by the senses or observed by instruments.

Activity

What is earthshine?[anno: Earthshine is the amount of the Sun's light that is not absorbed by Earth. This light is reflected by Earth back toward the Moon.]

What things alter the amount of earthshine?[anno: Conditions that alter the amount of earthshine are the amounts of clouds, atmospheric dust, and snow that are covering Earth.]

Draw a diagram showing the path of earthshine from the Sun to Earth and the Moon. Label all the parts of your diagram.[anno: Students' diagrams should show the Sun, Earth, and the Moon. Light travels from the Sun to Earth. Some of the light reflects off Earth's surface toward the Moon.]